1. Field of the Invention
The present invention generally relates to an image display apparatus, and particularly relates to a plasma display apparatus.
2. Description of the Related Art
A plasma display panel has two glass substrates which have electrodes formed thereon and define a space therebetween that is filled with discharge gas, and generates electric discharge by applying voltages between the electrodes so as to induce light emission from fluorescent substance provided on the substrates in response to the ultraviolet light generated by the electric discharge, thereby displaying an image. Plasma display panels are widely used as large-screen display apparatuses due to the facts that a large-sized screen is easy to make, that the self-light-emission nature ensures high display quality, and that the response speed is high.
On a display panel, X electrodes and Y electrodes extending in parallel are formed, and address electrodes are provided to run perpendicularly to the X and Y electrodes. The X and Y electrodes serve to generate sustain discharges for display-purpose light emission. The sustain discharges are generated by applying voltage pulses repeatedly between the X electrodes and the Y electrode. The Y electrodes also serve as scan electrodes for use in the writing of display data. The address electrodes serve to select discharge cells that emit light, and apply address-voltage pulses responsive to display data in order to generate write discharge for selecting the discharge cells between the Y electrodes and the address electrodes.
FIG. 1 is a block diagram showing a main part of a related-art plasma display apparatus. A plasma display apparatus shown in FIG. 1 includes a plasma display panel 11, an address-electrode drive circuit 12, a Y-electrode drive circuit 13, an X-electrode drive circuit 14, a scan circuit 15, a drive control circuit 16, a signal processing circuit 17, and an AC/DC power supply circuit 18.
The signal processing circuit 17 receives a clock signal, display data, a vertical synchronizing signal, a horizontal synchronizing signal, etc., which are supplied from an external source, and performs various tasks such as the writing of RGB display data to a frame memory in response to the vertical synchronizing signal. The drive control circuit 16 controls the address-electrode drive circuit 12, the Y-electrode drive circuit 13, the X-electrode drive circuit 14, and the scan circuit 15 to display the display data stored in the frame memory on the plasma display panel 11.
Specifically, the drive control circuit 16 generates address control signals responsive to the display data in the frame memory in synchronization with the clock signal. The address control signals are supplied to the address-electrode drive circuit 12. The drive control circuit 16 further generates scan driver control signals for controlling the scan circuit 15 in synchronization with the vertical synchronizing signal and the horizontal synchronizing signal. The scan driver control signals are supplied to the scan circuit 15. The drive control circuit 16 further drives the Y-electrode drive circuit 13 and the X-electrode drive circuit 14 in synchronization with the vertical synchronizing signal and the horizontal synchronizing signal.
The address-electrode drive circuit 12 applies address-voltage pulses responsive to the display data to address electrodes A1 through Am in synchronization with the clock signal. The Y-electrode drive circuit 13 drives Y electrodes Y1 through Yn independently of each other via the scan circuit 15. The X-electrode drive circuit 14 drives X electrodes X1 through Xn all together.
Through the operations of the address-electrode drive circuit 12, the Y-electrode drive circuit 13, the X-electrode drive circuit 14, and the scan circuit 15, each display pixel is initialized in a reset period, followed by an address period in which pixels to be displayed are selected, and, in a sustain period that comes last, the selected pixels are caused to emit light.
In the reset period, a reset/address-voltage generating circuit inside the Y-electrode drive circuit 13 generates a reset voltage, so that the scan circuit 15 applies the reset voltage to all the Y electrodes Y1 through Yn. Further, a reset voltage generated by a reset/address-voltage generating circuit inside the X-electrode drive circuit 14 is applied to all the X electrodes X1 through Xn.
In the address period, the scan circuit 15 drives the Y electrodes Y1 through Yn successively one by one based on the address voltage generated by the reset/address-voltage generating circuit of the Y-electrode drive circuit 13, and, in conjunction therewith, the address-electrode drive circuit 12 applies address-voltage pulses for one horizontal line responsive to the display data to the address electrodes A1 through Am. Cells to be displayed are selected in this manner, thereby controlling the display/non-display (selection/non-selection) of each display cell (pixel).
In the sustain period, sustain voltage pulses generated by a sustain-pulse circuit of the Y-electrode drive circuit 13 are applied to the Y electrodes Y1 through Yn via the scan circuit 15, and sustain voltage pulses generated by a sustain-pulse circuit of the X-electrode drive circuit 14 are applied to the X electrodes X1 through Xn. The application of these sustain voltage pulses generates sustain discharge between an X electrode and a Y electrode at the cells selected as display cells. These sustain voltage pulses are generated based on a sustain voltage VS0. The AC/DC power supply circuit 18 converts a commercial AC power supply voltage into a DC power supply voltage, which is supplied as the sustain voltage VS0 to the X-electrode drive circuit 14 via an electric cable 18a. Further, the sustain voltage VS0 is supplied from the X-electrode drive circuit 14 to the Y-electrode drive circuit 13 via an electric cable 18 b. 
FIG. 2 is a drawing showing an example of the configuration of the related-art AC/DC power supply circuit 18. The AC/DC power supply circuit 18 includes a rectifying circuit 21, a pulse generating circuit 22, a transformer 23, a diode 24, a light-emission device 25, a light-detection device 26, a smoothing condenser Cvs0, and resistors R1 and R2 serving as a voltage detection circuit.
The rectifying circuit 21 rectifies an AC voltage supplied from a commercial AC power supply, and supplies the rectified voltage to the pulse generating circuit 22. The pulse generating circuit 22 generates a rectangular-pulse voltage waveform based on the rectified voltage supplied from the rectifying circuit 21. This pulse voltage waveform causes an electric current to be generated at the output terminal of the transformer 23. This electric current flows into the smoothing condenser Cvs0 through the diode 24, thereby charging the smoothing condenser Cvs0. A voltage between the opposite ends of the smoothing condenser Cvs0 is divided by the resistors R1 and R2, so that the light-emission device 25 emits light with intensity responsive to the divided voltage level. The light-detection device 26 receives light from the light-emission device 25, and supplies a signal responsive to the intensity of the received light to the pulse generating circuit 22. The pulse generating circuit 22 controls the generation of the pulses in response to the signal from the light-detection device 26. This feedback control serves to adjust the voltage between the opposite ends of the smoothing condenser Cvs0 to a predetermined voltage (i.e., to the sustain discharge voltage VS0).
The transformer 23 transmits an electric power from the primary side to the secondary side via changes in magnetic flux, so that the input side and output side of the transformer 23 are not electrically connected with each other (i.e., not directly connected through an electrical conductor). An optical coupling unit 27 comprised of the light-emission device 25 and the light-detection device 26 transmits information from the input side to the output side via changes in light intensity, so that the input side and output side are not electrically connected with each other (i.e., not directly connected through an electrical conductor). In this manner, the primary side and the secondary side are electrically insulated from each other.
FIG. 3 is a drawing showing an example of the circuit configuration of the related-art X-electrode drive circuit 14. The X-electrode drive circuit 14 includes an energy-supply-purpose condenser Cvs1, power MOS-field-effect transistors Q1 through Q4, diodes D1 and D2, inductors L1 and L2, and a charge-collection-purpose condenser C1. An illustrated capacitance Cp1 represents the capacitance of the plasma display panel 11, and, in particular, is the capacitance of the X electrodes of the plasma display panel 11. What is shown in FIG. 3 is a portion corresponding to the sustain circuit for generating sustain discharges that is provided in the X-electrode drive circuit 14. The X-electrode drive circuit 14 further includes circuit portions for supplying the reset voltage and the like, which are omitted in FIG. 3.
At the initial stage of the performing of sustain discharge, the capacitor Cp1 has no electric charge accumulated therein and is placed at the ground potential while the charge-collection-purpose condenser C1 has accumulated electric charge and exhibits a voltage of about VS0/2. In this state, the power MOS-field-effect transistor Q3 is turned on to become conductive, so that the electric charge of the charge-collection-purpose condenser C1 flows into the capacitor Cp1 via the diode D1 and the inductor L1. As a result, the capacitor Cp1 exhibits a voltage of about VS0 through the resonance of the inductor L1 and the capacitor Cp1. Thereafter, in order to maintain the X electrodes of the plasma display panel 11 at a constant voltage, the power MOS-field-effect transistor Q1 is turned on to supply the voltage VS0 from the energy-supply-purpose condenser Cvs1 to the plasma display panel 11. Consequently, sustain discharge is generated. Here, the energy-supply-purpose condenser Cvs1 receives the sustain-discharge voltage VS0 supplied from the AC/DC power supply circuit 18.
After this, the power MOS-field-effect transistor Q1 is turned off, and the power MOS-field-effect transistor Q4 is turned on, so that electric charge flows into the charge-collection-purpose condenser C1 from the capacitor Cp1 via the inductor L2 and the diode D2. With this arrangement, the electric charge that has been used to charge the capacitor Cp1 of the plasma display panel 11 can be collected. The power MOS-field-effect transistor Q2 is then turned on to remove the electric charge of Cp1 remaining after the collection, thereby setting the X electrodes to the ground potential.
FIG. 4 is a drawing showing a connection between the X-electrode drive circuit 14 and the AC/DC power supply circuit 18 in the related-art configuration. In FIG. 4, the same elements as those of FIGS. 1 through 3 are referred to by the same numerals, and a description thereof will be omitted.
The AC/DC power supply circuit 18 is implemented on an AC/DC-power-supply circuit board 31. The X-electrode drive circuit 14 is implemented on an X-electrode-drive circuit board 32. The AC/DC-power-supply circuit board 31 and the X-electrode-drive circuit board 32 are separate boards, and the AC/DC power supply circuit 18 and the X-electrode drive circuit 14 on the respective boards are connected with each other via the electric cable 18a. 
In such a configuration, proper handling and storing of the electric cable 18a are necessary, and, also, a thick cable is required to supply a high voltage (VS0), which results in a cost increase. Further, since a voltage drop occurs when an electric current runs through the electric cable 18a, there is a need to provide the energy-supply-purpose condenser Cvs1 with a large capacity in the X-electrode drive circuit 14, which results in a need for a large circuit-board area.
FIG. 5 is a drawing showing the arrangement of circuits of a related-art plasma display apparatus. What is shown in FIG. 3 is the plasma display panel 11 as viewed from the rear. Various circuits are arranged on the backside (i.e., opposite the display screen side) of the plasma display panel 11.
The drive control circuit 16, the signal processing circuit 17, and the AC/DC power supply circuit 18 are arranged around the center of the plasma display panel 11, and the X-electrode drive circuit 14 and the Y-electrode drive circuit 13 are arranged on the opposite sides of the plasma display panel 11 in such a manner as to keep balance. The address-electrode drive circuit 12 is arranged at the bottom of the plasma display panel 11. The AC/DC power supply circuit 18 positioned at around the center supplies a power supply voltage to the X-electrode drive circuit 14 via the electric cable 18a. Further, the power supply voltage is supplied from the X-electrode drive circuit 14 to the Y-electrode drive circuit 13 via the electric cable 18 b. 
In the related-art configuration, there is a need to arrange the Y-electrode drive circuit 13, the X-electrode drive circuit 14, and the AC/DC power supply circuit 18 in such a manner as to keep proper balance between the left-hand side and the right-hand side as shown in FIG. 5 because these circuits are large and heavy. To this end, the required arrangement is such that the AC/DC power supply circuit 18 is positioned at the center, and supplies the power supply voltage via electric cables to the Y-electrode drive circuit 13 and the X-electrode drive circuit 14 positioned on the opposite sides, respectively. This arrangement, however, leads to a cost increase since a thick electric cable is necessary for the purpose of supplying a high voltage as previously described, and also requires a large circuit-board area since a voltage drop occurring upon the flowing of an electric current through the electric cable 18a necessitates the provision of the energy-supply-purpose condenser Cvs1 with a large capacity in the X-electrode drive circuit 14.
Moreover, there has been a trend in recent years for plasma display panels to have an increased panel size in response to the demand for large-size screen display, which results in a further increase in the length of the electric cable 18a. 
[Patent Document 1] Japanese Patent Application Publication No. 2003-302932
Accordingly, there is a need for a plasma display apparatus for which the cost of an electric cable required to supply a power is reduced, and for which the problem of a voltage drop occurring upon the flowing of an electric current through the electric cable is obviated.